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sent_packet_handler.go
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sent_packet_handler.go
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package ackhandler
import (
"errors"
"fmt"
"math"
"time"
"v2ray.com/core/external/github.com/lucas-clemente/quic-go/internal/congestion"
"v2ray.com/core/external/github.com/lucas-clemente/quic-go/internal/protocol"
"v2ray.com/core/external/github.com/lucas-clemente/quic-go/internal/qerr"
"v2ray.com/core/external/github.com/lucas-clemente/quic-go/internal/utils"
"v2ray.com/core/external/github.com/lucas-clemente/quic-go/internal/wire"
)
const (
// Maximum reordering in time space before time based loss detection considers a packet lost.
// In fraction of an RTT.
timeReorderingFraction = 1.0 / 8
// Timer granularity. The timer will not be set to a value smaller than granularity.
granularity = time.Millisecond
)
type sentPacketHandler struct {
lastSentPacketNumber protocol.PacketNumber
packetNumberGenerator *packetNumberGenerator
lastSentRetransmittablePacketTime time.Time
lastSentCryptoPacketTime time.Time
nextPacketSendTime time.Time
largestAcked protocol.PacketNumber
largestReceivedPacketWithAck protocol.PacketNumber
// lowestPacketNotConfirmedAcked is the lowest packet number that we sent an ACK for, but haven't received confirmation, that this ACK actually arrived
// example: we send an ACK for packets 90-100 with packet number 20
// once we receive an ACK from the peer for packet 20, the lowestPacketNotConfirmedAcked is 101
lowestPacketNotConfirmedAcked protocol.PacketNumber
packetHistory *sentPacketHistory
retransmissionQueue []*Packet
bytesInFlight protocol.ByteCount
congestion congestion.SendAlgorithm
rttStats *congestion.RTTStats
handshakeComplete bool
// The number of times the crypto packets have been retransmitted without receiving an ack.
cryptoCount uint32
// The number of times a PTO has been sent without receiving an ack.
ptoCount uint32
// The number of PTO probe packets that should be sent.
numProbesToSend int
// The time at which the next packet will be considered lost based on early transmit or exceeding the reordering window in time.
lossTime time.Time
// The alarm timeout
alarm time.Time
logger utils.Logger
}
// NewSentPacketHandler creates a new sentPacketHandler
func NewSentPacketHandler(
initialPacketNumber protocol.PacketNumber,
rttStats *congestion.RTTStats,
logger utils.Logger,
) SentPacketHandler {
congestion := congestion.NewCubicSender(
congestion.DefaultClock{},
rttStats,
false, /* don't use reno since chromium doesn't (why?) */
protocol.InitialCongestionWindow,
protocol.DefaultMaxCongestionWindow,
)
return &sentPacketHandler{
packetNumberGenerator: newPacketNumberGenerator(initialPacketNumber, protocol.SkipPacketAveragePeriodLength),
packetHistory: newSentPacketHistory(),
rttStats: rttStats,
congestion: congestion,
logger: logger,
}
}
func (h *sentPacketHandler) lowestUnacked() protocol.PacketNumber {
if p := h.packetHistory.FirstOutstanding(); p != nil {
return p.PacketNumber
}
return h.largestAcked + 1
}
func (h *sentPacketHandler) SetHandshakeComplete() {
h.logger.Debugf("Handshake complete. Discarding all outstanding crypto packets.")
var queue []*Packet
for _, packet := range h.retransmissionQueue {
if packet.EncryptionLevel == protocol.Encryption1RTT {
queue = append(queue, packet)
}
}
var cryptoPackets []*Packet
h.packetHistory.Iterate(func(p *Packet) (bool, error) {
if p.EncryptionLevel != protocol.Encryption1RTT {
cryptoPackets = append(cryptoPackets, p)
}
return true, nil
})
for _, p := range cryptoPackets {
h.packetHistory.Remove(p.PacketNumber)
}
h.retransmissionQueue = queue
h.handshakeComplete = true
}
func (h *sentPacketHandler) SentPacket(packet *Packet) {
if isRetransmittable := h.sentPacketImpl(packet); isRetransmittable {
h.packetHistory.SentPacket(packet)
h.updateLossDetectionAlarm()
}
}
func (h *sentPacketHandler) SentPacketsAsRetransmission(packets []*Packet, retransmissionOf protocol.PacketNumber) {
var p []*Packet
for _, packet := range packets {
if isRetransmittable := h.sentPacketImpl(packet); isRetransmittable {
p = append(p, packet)
}
}
h.packetHistory.SentPacketsAsRetransmission(p, retransmissionOf)
h.updateLossDetectionAlarm()
}
func (h *sentPacketHandler) sentPacketImpl(packet *Packet) bool /* isRetransmittable */ {
if h.logger.Debug() && h.lastSentPacketNumber != 0 {
for p := h.lastSentPacketNumber + 1; p < packet.PacketNumber; p++ {
h.logger.Debugf("Skipping packet number %#x", p)
}
}
h.lastSentPacketNumber = packet.PacketNumber
if len(packet.Frames) > 0 {
if ackFrame, ok := packet.Frames[0].(*wire.AckFrame); ok {
packet.largestAcked = ackFrame.LargestAcked()
}
}
packet.Frames = stripNonRetransmittableFrames(packet.Frames)
isRetransmittable := len(packet.Frames) != 0
if isRetransmittable {
if packet.EncryptionLevel != protocol.Encryption1RTT {
h.lastSentCryptoPacketTime = packet.SendTime
}
h.lastSentRetransmittablePacketTime = packet.SendTime
packet.includedInBytesInFlight = true
h.bytesInFlight += packet.Length
packet.canBeRetransmitted = true
if h.numProbesToSend > 0 {
h.numProbesToSend--
}
}
h.congestion.OnPacketSent(packet.SendTime, h.bytesInFlight, packet.PacketNumber, packet.Length, isRetransmittable)
h.nextPacketSendTime = utils.MaxTime(h.nextPacketSendTime, packet.SendTime).Add(h.congestion.TimeUntilSend(h.bytesInFlight))
return isRetransmittable
}
func (h *sentPacketHandler) ReceivedAck(ackFrame *wire.AckFrame, withPacketNumber protocol.PacketNumber, encLevel protocol.EncryptionLevel, rcvTime time.Time) error {
largestAcked := ackFrame.LargestAcked()
if largestAcked > h.lastSentPacketNumber {
return qerr.Error(qerr.InvalidAckData, "Received ACK for an unsent package")
}
// duplicate or out of order ACK
if withPacketNumber != 0 && withPacketNumber < h.largestReceivedPacketWithAck {
h.logger.Debugf("Ignoring ACK frame (duplicate or out of order).")
return nil
}
h.largestReceivedPacketWithAck = withPacketNumber
h.largestAcked = utils.MaxPacketNumber(h.largestAcked, largestAcked)
if !h.packetNumberGenerator.Validate(ackFrame) {
return qerr.Error(qerr.InvalidAckData, "Received an ACK for a skipped packet number")
}
if rttUpdated := h.maybeUpdateRTT(largestAcked, ackFrame.DelayTime, rcvTime); rttUpdated {
h.congestion.MaybeExitSlowStart()
}
ackedPackets, err := h.determineNewlyAckedPackets(ackFrame)
if err != nil {
return err
}
if len(ackedPackets) == 0 {
return nil
}
priorInFlight := h.bytesInFlight
for _, p := range ackedPackets {
// TODO(#1534): check the encryption level
// if encLevel < p.EncryptionLevel {
// return fmt.Errorf("Received ACK with encryption level %s that acks a packet %d (encryption level %s)", encLevel, p.PacketNumber, p.EncryptionLevel)
// }
// largestAcked == 0 either means that the packet didn't contain an ACK, or it just acked packet 0
// It is safe to ignore the corner case of packets that just acked packet 0, because
// the lowestPacketNotConfirmedAcked is only used to limit the number of ACK ranges we will send.
if p.largestAcked != 0 {
h.lowestPacketNotConfirmedAcked = utils.MaxPacketNumber(h.lowestPacketNotConfirmedAcked, p.largestAcked+1)
}
if err := h.onPacketAcked(p, rcvTime); err != nil {
return err
}
if p.includedInBytesInFlight {
h.congestion.OnPacketAcked(p.PacketNumber, p.Length, priorInFlight, rcvTime)
}
}
if err := h.detectLostPackets(rcvTime, priorInFlight); err != nil {
return err
}
h.ptoCount = 0
h.cryptoCount = 0
h.updateLossDetectionAlarm()
return nil
}
func (h *sentPacketHandler) GetLowestPacketNotConfirmedAcked() protocol.PacketNumber {
return h.lowestPacketNotConfirmedAcked
}
func (h *sentPacketHandler) determineNewlyAckedPackets(ackFrame *wire.AckFrame) ([]*Packet, error) {
var ackedPackets []*Packet
ackRangeIndex := 0
lowestAcked := ackFrame.LowestAcked()
largestAcked := ackFrame.LargestAcked()
err := h.packetHistory.Iterate(func(p *Packet) (bool, error) {
// Ignore packets below the lowest acked
if p.PacketNumber < lowestAcked {
return true, nil
}
// Break after largest acked is reached
if p.PacketNumber > largestAcked {
return false, nil
}
if ackFrame.HasMissingRanges() {
ackRange := ackFrame.AckRanges[len(ackFrame.AckRanges)-1-ackRangeIndex]
for p.PacketNumber > ackRange.Largest && ackRangeIndex < len(ackFrame.AckRanges)-1 {
ackRangeIndex++
ackRange = ackFrame.AckRanges[len(ackFrame.AckRanges)-1-ackRangeIndex]
}
if p.PacketNumber >= ackRange.Smallest { // packet i contained in ACK range
if p.PacketNumber > ackRange.Largest {
return false, fmt.Errorf("BUG: ackhandler would have acked wrong packet 0x%x, while evaluating range 0x%x -> 0x%x", p.PacketNumber, ackRange.Smallest, ackRange.Largest)
}
ackedPackets = append(ackedPackets, p)
}
} else {
ackedPackets = append(ackedPackets, p)
}
return true, nil
})
if h.logger.Debug() && len(ackedPackets) > 0 {
pns := make([]protocol.PacketNumber, len(ackedPackets))
for i, p := range ackedPackets {
pns[i] = p.PacketNumber
}
h.logger.Debugf("\tnewly acked packets (%d): %#x", len(pns), pns)
}
return ackedPackets, err
}
func (h *sentPacketHandler) maybeUpdateRTT(largestAcked protocol.PacketNumber, ackDelay time.Duration, rcvTime time.Time) bool {
if p := h.packetHistory.GetPacket(largestAcked); p != nil {
h.rttStats.UpdateRTT(rcvTime.Sub(p.SendTime), ackDelay, rcvTime)
if h.logger.Debug() {
h.logger.Debugf("\tupdated RTT: %s (σ: %s)", h.rttStats.SmoothedRTT(), h.rttStats.MeanDeviation())
}
return true
}
return false
}
func (h *sentPacketHandler) updateLossDetectionAlarm() {
// Cancel the alarm if no packets are outstanding
if !h.packetHistory.HasOutstandingPackets() {
h.alarm = time.Time{}
return
}
if h.packetHistory.HasOutstandingCryptoPackets() {
h.alarm = h.lastSentCryptoPacketTime.Add(h.computeCryptoTimeout())
} else if !h.lossTime.IsZero() {
// Early retransmit timer or time loss detection.
h.alarm = h.lossTime
} else { // PTO alarm
h.alarm = h.lastSentRetransmittablePacketTime.Add(h.computePTOTimeout())
}
}
func (h *sentPacketHandler) detectLostPackets(now time.Time, priorInFlight protocol.ByteCount) error {
h.lossTime = time.Time{}
maxRTT := float64(utils.MaxDuration(h.rttStats.LatestRTT(), h.rttStats.SmoothedRTT()))
delayUntilLost := time.Duration((1.0 + timeReorderingFraction) * maxRTT)
var lostPackets []*Packet
h.packetHistory.Iterate(func(packet *Packet) (bool, error) {
if packet.PacketNumber > h.largestAcked {
return false, nil
}
timeSinceSent := now.Sub(packet.SendTime)
if timeSinceSent > delayUntilLost {
lostPackets = append(lostPackets, packet)
} else if h.lossTime.IsZero() {
if h.logger.Debug() {
h.logger.Debugf("\tsetting loss timer for packet %#x to %s (in %s)", packet.PacketNumber, delayUntilLost, delayUntilLost-timeSinceSent)
}
// Note: This conditional is only entered once per call
h.lossTime = now.Add(delayUntilLost - timeSinceSent)
}
return true, nil
})
if h.logger.Debug() && len(lostPackets) > 0 {
pns := make([]protocol.PacketNumber, len(lostPackets))
for i, p := range lostPackets {
pns[i] = p.PacketNumber
}
h.logger.Debugf("\tlost packets (%d): %#x", len(pns), pns)
}
for _, p := range lostPackets {
// the bytes in flight need to be reduced no matter if this packet will be retransmitted
if p.includedInBytesInFlight {
h.bytesInFlight -= p.Length
h.congestion.OnPacketLost(p.PacketNumber, p.Length, priorInFlight)
}
if p.canBeRetransmitted {
// queue the packet for retransmission, and report the loss to the congestion controller
if err := h.queuePacketForRetransmission(p); err != nil {
return err
}
}
h.packetHistory.Remove(p.PacketNumber)
}
return nil
}
func (h *sentPacketHandler) OnAlarm() error {
// When all outstanding are acknowledged, the alarm is canceled in
// updateLossDetectionAlarm. This doesn't reset the timer in the session though.
// When OnAlarm is called, we therefore need to make sure that there are
// actually packets outstanding.
if h.packetHistory.HasOutstandingPackets() {
if err := h.onVerifiedAlarm(); err != nil {
return err
}
}
h.updateLossDetectionAlarm()
return nil
}
func (h *sentPacketHandler) onVerifiedAlarm() error {
var err error
if h.packetHistory.HasOutstandingCryptoPackets() {
if h.logger.Debug() {
h.logger.Debugf("Loss detection alarm fired in crypto mode. Crypto count: %d", h.cryptoCount)
}
h.cryptoCount++
err = h.queueCryptoPacketsForRetransmission()
} else if !h.lossTime.IsZero() {
if h.logger.Debug() {
h.logger.Debugf("Loss detection alarm fired in loss timer mode. Loss time: %s", h.lossTime)
}
// Early retransmit or time loss detection
err = h.detectLostPackets(time.Now(), h.bytesInFlight)
} else { // PTO
if h.logger.Debug() {
h.logger.Debugf("Loss detection alarm fired in PTO mode. PTO count: %d", h.ptoCount)
}
h.ptoCount++
h.numProbesToSend += 2
}
return err
}
func (h *sentPacketHandler) GetAlarmTimeout() time.Time {
return h.alarm
}
func (h *sentPacketHandler) onPacketAcked(p *Packet, rcvTime time.Time) error {
// This happens if a packet and its retransmissions is acked in the same ACK.
// As soon as we process the first one, this will remove all the retransmissions,
// so we won't find the retransmitted packet number later.
if packet := h.packetHistory.GetPacket(p.PacketNumber); packet == nil {
return nil
}
// only report the acking of this packet to the congestion controller if:
// * it is a retransmittable packet
// * this packet wasn't retransmitted yet
if p.isRetransmission {
// that the parent doesn't exist is expected to happen every time the original packet was already acked
if parent := h.packetHistory.GetPacket(p.retransmissionOf); parent != nil {
if len(parent.retransmittedAs) == 1 {
parent.retransmittedAs = nil
} else {
// remove this packet from the slice of retransmission
retransmittedAs := make([]protocol.PacketNumber, 0, len(parent.retransmittedAs)-1)
for _, pn := range parent.retransmittedAs {
if pn != p.PacketNumber {
retransmittedAs = append(retransmittedAs, pn)
}
}
parent.retransmittedAs = retransmittedAs
}
}
}
// this also applies to packets that have been retransmitted as probe packets
if p.includedInBytesInFlight {
h.bytesInFlight -= p.Length
}
if err := h.stopRetransmissionsFor(p); err != nil {
return err
}
return h.packetHistory.Remove(p.PacketNumber)
}
func (h *sentPacketHandler) stopRetransmissionsFor(p *Packet) error {
if err := h.packetHistory.MarkCannotBeRetransmitted(p.PacketNumber); err != nil {
return err
}
for _, r := range p.retransmittedAs {
packet := h.packetHistory.GetPacket(r)
if packet == nil {
return fmt.Errorf("sent packet handler BUG: marking packet as not retransmittable %d (retransmission of %d) not found in history", r, p.PacketNumber)
}
h.stopRetransmissionsFor(packet)
}
return nil
}
func (h *sentPacketHandler) DequeuePacketForRetransmission() *Packet {
if len(h.retransmissionQueue) == 0 {
return nil
}
packet := h.retransmissionQueue[0]
// Shift the slice and don't retain anything that isn't needed.
copy(h.retransmissionQueue, h.retransmissionQueue[1:])
h.retransmissionQueue[len(h.retransmissionQueue)-1] = nil
h.retransmissionQueue = h.retransmissionQueue[:len(h.retransmissionQueue)-1]
return packet
}
func (h *sentPacketHandler) DequeueProbePacket() (*Packet, error) {
if len(h.retransmissionQueue) == 0 {
p := h.packetHistory.FirstOutstanding()
if p == nil {
return nil, errors.New("cannot dequeue a probe packet. No outstanding packets")
}
if err := h.queuePacketForRetransmission(p); err != nil {
return nil, err
}
}
return h.DequeuePacketForRetransmission(), nil
}
func (h *sentPacketHandler) PeekPacketNumber() (protocol.PacketNumber, protocol.PacketNumberLen) {
pn := h.packetNumberGenerator.Peek()
return pn, protocol.GetPacketNumberLengthForHeader(pn, h.lowestUnacked())
}
func (h *sentPacketHandler) PopPacketNumber() protocol.PacketNumber {
return h.packetNumberGenerator.Pop()
}
func (h *sentPacketHandler) SendMode() SendMode {
numTrackedPackets := len(h.retransmissionQueue) + h.packetHistory.Len()
// Don't send any packets if we're keeping track of the maximum number of packets.
// Note that since MaxOutstandingSentPackets is smaller than MaxTrackedSentPackets,
// we will stop sending out new data when reaching MaxOutstandingSentPackets,
// but still allow sending of retransmissions and ACKs.
if numTrackedPackets >= protocol.MaxTrackedSentPackets {
if h.logger.Debug() {
h.logger.Debugf("Limited by the number of tracked packets: tracking %d packets, maximum %d", numTrackedPackets, protocol.MaxTrackedSentPackets)
}
return SendNone
}
if h.numProbesToSend > 0 {
return SendPTO
}
// Only send ACKs if we're congestion limited.
if cwnd := h.congestion.GetCongestionWindow(); h.bytesInFlight > cwnd {
if h.logger.Debug() {
h.logger.Debugf("Congestion limited: bytes in flight %d, window %d", h.bytesInFlight, cwnd)
}
return SendAck
}
// Send retransmissions first, if there are any.
if len(h.retransmissionQueue) > 0 {
return SendRetransmission
}
if numTrackedPackets >= protocol.MaxOutstandingSentPackets {
if h.logger.Debug() {
h.logger.Debugf("Max outstanding limited: tracking %d packets, maximum: %d", numTrackedPackets, protocol.MaxOutstandingSentPackets)
}
return SendAck
}
return SendAny
}
func (h *sentPacketHandler) TimeUntilSend() time.Time {
return h.nextPacketSendTime
}
func (h *sentPacketHandler) ShouldSendNumPackets() int {
if h.numProbesToSend > 0 {
// RTO probes should not be paced, but must be sent immediately.
return h.numProbesToSend
}
delay := h.congestion.TimeUntilSend(h.bytesInFlight)
if delay == 0 || delay > protocol.MinPacingDelay {
return 1
}
return int(math.Ceil(float64(protocol.MinPacingDelay) / float64(delay)))
}
func (h *sentPacketHandler) queueCryptoPacketsForRetransmission() error {
var cryptoPackets []*Packet
h.packetHistory.Iterate(func(p *Packet) (bool, error) {
if p.canBeRetransmitted && p.EncryptionLevel != protocol.Encryption1RTT {
cryptoPackets = append(cryptoPackets, p)
}
return true, nil
})
for _, p := range cryptoPackets {
h.logger.Debugf("Queueing packet %#x as a crypto retransmission", p.PacketNumber)
if err := h.queuePacketForRetransmission(p); err != nil {
return err
}
}
return nil
}
func (h *sentPacketHandler) queuePacketForRetransmission(p *Packet) error {
if !p.canBeRetransmitted {
return fmt.Errorf("sent packet handler BUG: packet %d already queued for retransmission", p.PacketNumber)
}
if err := h.packetHistory.MarkCannotBeRetransmitted(p.PacketNumber); err != nil {
return err
}
h.retransmissionQueue = append(h.retransmissionQueue, p)
return nil
}
func (h *sentPacketHandler) computeCryptoTimeout() time.Duration {
duration := utils.MaxDuration(2*h.rttStats.SmoothedOrInitialRTT(), granularity)
// exponential backoff
// There's an implicit limit to this set by the crypto timeout.
return duration << h.cryptoCount
}
func (h *sentPacketHandler) computePTOTimeout() time.Duration {
// TODO(#1236): include the max_ack_delay
duration := utils.MaxDuration(h.rttStats.SmoothedOrInitialRTT()+4*h.rttStats.MeanDeviation(), granularity)
return duration << h.ptoCount
}